The long-term goals of this project are to understand how cell-to-cell signaling systems interface with regionally expressed transcription factors during development to generate correctly proportioned and patterned body parts. The experimental system that will be used is the fruit fly, Drosophila melanogaster. The starting point for these experiments are two genes, homothorax and extradenticle, that are important for specifying the identity of the proximal portion of the appendages in flies. These genes appear to limit or modify the activities of signaling pathways known to operate during appendage development. Both extradenticle and homothorax encode homeodomain-containing transcription factors. However, Extradenticle protein is only nuclear in the presence of Homothorax. In several tissues, Homothorax and Extradenticle are co-expressed with a Zn-finger-containing transcription factor encoded by the teashirt gene and, in the eye, these three proteins are co-expressed with another homeodomain protein encoded by the eyeless gene.The specific aims for this funding period are to: (1) determine the mechanism by which Extradenticle's nuclear localization is controlled by Homothorax, (2) characterize the roles of homothorax and teashirt in wing and eye development, (3) characterize the genes involved in repressing hth expression during leg development, and (4) characterize the role of novel genes, identified by a forward genetic screen, in proximo-distal patterning in the fly appendages. homothorax and extradenticle both have vertebrate homologs that, when misexpressed, can contribute to leukemias, suggesting that they also play a role in regulating growth and development in vertebrates. In addition, the transcriptional and post-transcriptional regulation of these factors appears similar in vertebrate and fly limb development, suggesting that many of their functions may also be conserved. An understanding of their basic functions in fly development should therefore generate information that is relevant to leukemia, as well as to defects that can occur in vertebrate limb development.